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Home > Publications > International Concrete Abstracts Portal
Showing 1-5 of 20 Abstracts search results
Document:
SP76-05
Date:
October 1, 1982
Author(s):
Heinrich Trost
Publication:
Symposium Papers
Volume:
76
Abstract:
The proposed calculation procedure is based on a reference deflection at the interesting point of the uncracked concrete member. This reference deflection is calculated on the basis of the existing distribution of the gross section stiffness-in analogy to the usual determination of the design forces in statically indeterminate systems-- as available from tables or handbooks. Then this reference value, either for the maximum service load or for the sustained load when time-dependent effects are concerned, is multiplied by reinforcement-dependent coefficients given in figures or calculable from closed formulae in order to obtain the initial deflection and the time-dependent deflection due to creep and shrinkage. The probable deflection, as the prognostic value of interest and in which the deflection-reducing effect of the reinforcement and the tension stiffening is considered, is determined by interpolation between the deflections in the limit states according to the acting moment level.
DOI:
10.14359/6786
SP76-06
G. Chadha
A precise evaluation of prestress losses in prestressed concrete members is a simple but time-consuming problem. Nevertheless, design aids would be useful to engineers. This paper uses an iterative procedure for calculating the long-term losses. Tables for direct prediction of losses due to creep and shrinkage are presented. It uses available information on concrete creep and shrinkage and steel stress relaxation, and includes the effect of interaction of various factors contributing to the prestress losses. To illustrate the use of the tables, two numerical examples are included. The tables are applicable for all prestressed concrete structures such as buildings, bridges, or nuclear power plants. The manual computations being tedious and time consuming, the predicted prestress losses tables are highly accurate, as they are based on interaction computer program using increments of short duration.
10.14359/6787
SP76-07
M. S. Khalil, W. H. Dilger, and A. Ghali
A computer-aided, step-by-step method is presented for the study of time-dependent stresses and deformations of pre-stressed concrete frames. The method is used to investigate the effectiveness of deferring the final connections between column or walls and slabs in building frames and allowing the slabs to slide on the columns during post-tensioning. The joints are then constructed at a later date. A second investigation concentrates on the stresses developed in a cast-in-place, normally-reinforced closure strip cast sometime after post-tensioning of the floors in a long continuous frame. Results obtained for the two examples are evaluated and the possibility of excessive stresses and cracking is discussed.
10.14359/6788
SP76-08
Marwan A. Daye
Creep of concrete is an important characteristic to the 1' design engineer particularly when dealing with prestressed concrete, more so in the design of prestressed reactor/containment buildings. Since actual testing is a long term process, an empirical formula for prediction of creep of concrete is developed. The effect of the physical properties of the aggregate and the mix proportions as well as the age at loading and the concrete temperature are considered. Creep test results for cylinders made from both normal and light weight concrete are compared with creep values predicted using the developed formula. The comparison indicated good correlation between both values. The prediction formula is computerized such that the creep values for a concrete mix could be evaluated immediately with the input of the mix properties on three computer data cards.
10.14359/6789
SP76-09
Lauge Fuglsang Nielsen
In the first part of the present paper, the so-called Improved Dischinger Method, developed by the author, is identified as belonging to a class of methods which reflects the mechanical behavior of concrete in a reliable way, consistent with the assumption of linear viscoelasticity. At the same time, the basis of some other well-known methods is evaluated. In the second part of the paper, the class of methods mentioned above is evaluated with respect to practical applicability. Among other things, two features are hereby demonstrated which are much appreciated in practice, and which do not apply to any method: (1) The user has the choice of handling his problem on the basis of one of three consistent, analytically-determined alternative formulations of the stress strain relation; (2) Standard solutions may be developed which apply to any concrete. Finally, it is demonstrated how the Improved Dischinger Method may be used in "hand design" of concrete structures.
10.14359/6790
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